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-   -   RedGard over Schluter Kerdi membrane? (https://www.johnbridge.com/vbulletin/showthread.php?t=127498)

Biggycat 05-10-2019 10:35 PM

RedGard over Schluter Kerdi membrane?
Hey All! Good to be here looking for some input. Been lurking and this is my first post/question.

I am a DYI and doing my first shower pan. Installed the Schluter pre-sloped foam tray and curb onto new plywood subfloor using Laticrete 254 Platinum (polymer modified thinset mortar). Good adhesion, no complaints. Then I installed the Kerdi "waterproof" membrane and corners and Kerdi-band strips, all according to their instructions, using DitraSet (unmodified thinset mortar). Full coverage, removed air pockets. This all seemed to go smoothly. The DitraSet is very similar to work with as the Laticrete 254, smooth, creamy and sticky. Great. I let it stand for several days and then did a 24 hour water leak test. No leakage. However, the Kerdi membrane stayed wet for several hours after I drained the pan. I thought this stuff was gonna let all the water run right off, but it absorbed and stay moist. Is this normal? Has anyone had any experience with this after a leak test? I am VERY tempted to give the whole tray, all the Kerdi membrane material, a good coat of Red Guard, and don't see how this could hurt anything. It might void any warranty, but what could possibly be bad about more waterproofing?

jadnashua 05-10-2019 10:57 PM

If it didn't leak, you should be golden. Unless you have excess thinset in the seams, generally, moisture doesn't wick more than about 1/4-1/2" into the seam during a flood test, and if you did it right, there's at least a 2" overlap. Once completed, with the tile and grout, very little moisture gets to the membrane, and it generally evaporates back out in between showers. Excess thinset on top of the Kerdi isn't really a problem...it would be covered completely when adding tile...it's the between the sheets at a seam where excessive amounts might be a problem, or a gap.

While some have done what you're suggesting, there's no long-term validation of that method by either of the two manufacturers, so you become your own experimenter. IMHO, it's harder to get a nice even coat of a liquid applied waterproofing without runs or pinholes than making a sheet membrane waterproof.

A flood test is by far a worst case test. You'll never see that much standing water again in the shower. Water pressure goes up at about 0.43#/foot, so say 2" of standing water, that's way less than 0.1# of pressure, and maybe 1/4" on top of the tile is way less. There won't be room for much of any liquid water on the bottom of the tile, so the pressure would be miniscule (measurable in a test, but not without highly sensitive test equipment). IOW, don't worry about it.

Kman 05-11-2019 12:23 AM

Welcome to the forum, Ronny. :)

What you're seeing is normal. No need to go over it with anything else.

Gozo 05-11-2019 04:19 AM

I’m a DIY’er just like yourself and did my shower construction much like you have done so far. The bits of moisture hanging on to the Kerdi face is normal and mostly due to surface tension and capillary action. The membrane’s purpose is waterproofing, not so much to be water repellent. I’m in full agreement with Jim and Kevin to call it a success and not try to invent your own hybrid method. You’re more likely to create additional problems down the road than prevent something. We’ve been using ours for a year and a half now and it dries out likity-split.
As to your question “what could possibly be bad about more waterproofing?”, what Jim hinted to on pinholes is it. Unless you go thick enough to eliminate these for sure; water will work in the hole and could cause a blister and delamination of the Redgard from the Kerdi. The tile is bonded to the Redgard and could cause a loose tile. If pull it out to fix it, you’ll spread the delamination to the adjacent tiles. Why spend money just to make problems. That’s what family is for.

Biggycat 05-11-2019 09:31 AM

Jim, Kevin and Jeff, thank you very much!
I really appreciate your honest input and the benefits of your experience and skills. Looking forward to setting the tile. I might even post photos if it ends up nice.

Tool Guy - Kg 05-11-2019 07:24 PM


Originally Posted by Biggycat
...I might even post photos if it ends up nice.

...then I predict that you will be posting photos, Ronny. :tup2:

Biggycat 05-19-2019 10:23 PM

Questions about grout, caulk. And DitraSet vs. Laticrete 254
Is it recommended to lay in a nice bead of caulk in the plane change joints and then grout? Or grout first and then caulk? Does it matter?

Also, I am getting ready to tile the floor, Schluter tray with Kerdi membrane. I have DitraSet and I've set many a tile with it. However, I have been working with Laticrete 254 Platinum and am very impressed. The 254 is very sticky and sets hard like DitraSet can only dream about. It is specified for wet and underwater installations. So I am interested in setting the shower floor tile using the Laticrete 254. Would like some feedback from forum members. Thank you!

cx 05-19-2019 11:31 PM

You want to grout first, leaving the change of plane joints empty and clean, let the grout cure for a day, then apply your flexible sealant.

The DitraSet is more than adequate for setting your shower floor tiles. Up to you what you wanna use.

Keep in mind that the tile industry standards require that the shear bond of thinset mortar to a direct bonded waterproofing membrane be at least 50psi. You can use a mortar that advertises that it has shear bond of 100psi, or you can use one that advertises that it has shear bond of 400psi, and the requirement for bonding to the Kerdi is still 50psi.

My opinion; worth price charged.

Kman 05-19-2019 11:31 PM

Ronny, let's keep all questions related to this project on this thread, so that the history is in one place, and the questions and answers aren't duplicated. :)

Grout first, then caulk. Just do whatever you need to to keep grout out of those joints, let the grout dry overnight, and caulk the next day.

254 is a good mortar, the only thing is you'll probably need to allow some extra time for it to dry before grouting. You'll lose your warranty from Schluter, if that's an issue for you.

makethatkerdistick 05-20-2019 07:22 AM

Ronny, when you pick your sealant, make sure to choose 100% silicone and avoid the so-called "siliconized" ones. Those will shrink and crack and age prematurely while the silicone will last much longer in that sort of environment, even though it's a bit of a pain to apply it.
It's also worthwhile to consider silicones that are specially formulated for wet environments such as the ones which have "Microban." The claim is that they resist the growth of mold better.
Depending on the grout you choose, the manufacturer might offer a color-matched sealant.

Ideally, you want to at least squeegee your shower after every use to reduce mold growth potential (that's what I do). Some even towel-dry their showers to prevent mold completely. In addition to adequate ventilation, that's a long-term guarantee for trouble-free shower performance.

Biggycat 05-20-2019 09:01 PM

CX, Kman and Wolfgang, thank you for your answers! I just want you to know I truly appreciate your replies. You all give me more certainty, and make my project more fun, interesting and rewarding.

jadnashua 05-21-2019 07:38 PM

If your tile isn't set yet, and you want to avoid caulk entirely, choose an engineered profile instead. Can't be added after the fact, but works great during tiling.

Biggycat 05-28-2019 07:33 AM

...one more question about grout vs. caulk
Am getting closer to setting the floor tile in the shower. :oyeah: However, reading other threads about grout vs. caulk at the perimeter where the wall meets the floor, this seems to be an ongoing debate. I am confused. The floor is lined with Kerdi Membrane. I am leaning towards grout all around this perimeter. It seems to me that the drainage and moisture evaporation would be more efficient than if having a bead of caulk there. Looking forward to hearing from others regarding this issue. Thanks.

speed51133 05-28-2019 07:39 AM

What post recommends grout where the floor meets the wall?? I was unaware of ANY debate in this simple subject.

Per the tile industry standards, it is always caulk. Maybe you can find "some guy" that grouts it, but I highly doubt that person is on this forum. In the end, it is your bathroom. You can pack soil in that joint and plant grass if you want to, but the accepted standard is caulk.

MisterJJ 05-28-2019 08:16 AM

I'm certain that one of the regulars here has said that he always grouts these joints because it looks better. I did it and I'm super glad I did. I used "color-matched" caulk on the tile to drywall joints and tile to bathroom floor. The color of the caulk is definitely darker than the regular grout. It doesn't look terrible around the perimeter but it would look awful if I used it on all the joints where it is "required".

I've only used the shower for a few months, but so far so good. Also, I used Flexcolor CQ, which seems to be less brittle than regular grout, so hopefully less prone to cracking. But, to be honest, I won't know the long term durability since I'm selling the home soon and moving to Phoenix.

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